Controls on and the effect of extensional fault evolution in a transected rift setting, Northern North Sea

Download

Date

Author

Metadata

Abstract

The East Shetland Basin is a superb natural laboratory in which to study the
role that normal fault growth and linkage has in determining petroleum
prospectivity. Use of several high density 3D seismic volumes and over 250
boreholes permits key aspects of the Late Jurassic rift and its Permo-Triassic
precursor to be analysed and its role on hydrocarbon trap formation,
reservoir distribution and migration determined. The regional interpretation
has revealed the generation of a North Sea archipelago of Upper Jurassic
islands, the role of relay ramps in controlling syn-rift sediment dispersal
patterns and the impact of normal faults of the later episode crossing and
offsetting those generated by the earlier phase. The uplift, erosion and
meteoric flushing of Upper Jurassic and older strata within the exposed fault
blocks could potentially have huge consequences for the Brent play by
enhancing reservoir properties and hence, help identify new play
opportunities down-dip of major structures. Fault control on sediment
dispersal can also be documented in a more localized study on the Cladhan
Field, the site of a pronounced basin-margin relay ramp. This recent
discovered set of syn-rift density flows illustrates how the development and
distribution of depositional gradients and transport pathways form subtle
play types. The Cladhan area is just one of several locations throughout the
East Shetland Basin where the interaction of multiple rift phases is influential
in the structural feedback after the Upper Jurassic rifting event. The delicate
interaction and reactivation of underlying structural trends creates a series of
multi-tiered fault block systems which can define several aspects of a
petroleum system, depending upon the strike, polarity and level of
reactivation of faults from one rift to another. The observations of fault
growth and linkage in the Northern North Sea may provide generic lessons
that help in determining petroleum prospectivity in other hydrocarbon rift
basins (e.g. E. Africa and the N. Atlantic seaboard of North America)